Electric motors are used in various household, office, automotive, and industrial applications. A typical electric motor includes a rotor surrounded by an electromagnet, called a stator. When varying electrical energy is applied to the stator, a magnetic field is generated that produces a torque that spins the rotor. The rotor includes an output shaft that connects to an output device, such as a pump, fan, belt, or gear, to operate the device with the rotational output of the motor. A vertically mounted electric motor is one in which the output shaft is oriented vertically to enable the output shaft to be coupled to an output device positioned above or below the motor. Vertical motors rest on a stand, which is configured to provide a stable platform for the motor and output device. Horizontally oriented motors, on the other hand, are mounted such that the output shaft extends from the motor housing horizontally and the output shaft couples to an output device located next to the horizontal motor.
During operation of an electric motor, the rotating components of the motor and the driven components generate vibrations that resonate at various frequencies. A motor and housing system has a resonance frequency (also known as a reed-critical frequency or “RCF”), which is a function of the mass, distribution of the mass, and base geometry of the motor and housing system. If the frequency of the vibrations produced in the motor and driven equipment is close to or the same as the RCF of the combined system (motor and housing plus the driven equipment), the vibrations are amplified through the combined system, generating loud noises and potentially resulting in mechanical issues with the motor and system components.
The frequency of the vibrations and the RCF can be calculated in a motor based on the operating conditions of the motor and the geometry of the motor and housing system. Thus, combined system including a motor and driven equipment is typically designed such that the system RCF is not near the vibration frequencies of the combined system. However, in some instances, issues develop after installation of a vertical or horizontal motor that arise from changed operating conditions or erroneous calculations. One solution to RCF vibration issues involves replacing the motor with a motor of a different size, which produces different vibration frequencies and has a different RCF. Another solution is to replace the motor stand, which also alters the RCF of the combined system. However, both solutions require removing the motor from the stand. Vertical and horizontal motors in industrial applications are often very large and heavy, and heavy equipment is required to remove the motor from the stand. Thus, replacing the motor or stand can be very expensive. Consequently, an improved solution to RCF vibration issues is desirable.